Field of the Invention
The invention is based on the object of specifying a controllable resistor network which has a wide dynamic range and, at the same time, only a small relative resistance increment size.
Accordingly, according to the invention, a controllable resistor network is provided in which the respective resistance value of the resistor network can be selected from a predetermined group of discrete resistance values by means of control signals (XXX, YYY) which can be applied to the resistor network, the graduation of the resistance values exhibiting a logarithmic or a quasi-logarithmic characteristic.
An essential advantage of the controllable resistor network according to the invention consists in that a relatively wide dynamic range is achieved due to the logarithmic or quasi-logarithmic characteristic of the resistance graduation.
A second essential advantage of the resistor network according to the invention consists in that, due to the logarithmic or quasi-logarithmic characteristic of the resistance graduation, an extremely small number of control signals or control bits is required. This is associated with the fact that, in the resistor network according to the invention, the number of required switching elements or of required control lines is also small.
According to an advantageous development of the controllable resistor network, it is provided that the resistance values are graduated in such a manner that they form a predetermined number of resistance intervals having in each case the same number of resistance values. The resistance values within their respective resistance interval increase linearly or logarithmically; the resistance ranges covered by the resistance intervals in each case, in contrast, increase logarithmically toward rising resistance values. A first group of control signals selects the respective resistance interval and a second group of control signals determines one of the resistance values of the resistance interval selected in each case.
A first advantage of the advantageous development of the resistor network consists in that a relatively wide dynamic range is achieved due to the logarithmic increase or growth in resistance intervals.
A second advantage of the advantageous development of the resistor network can be seen in the fact that, in spite of the relatively wide dynamic range, a relatively small resistance increment size is achieved; in the resistor network according to the invention, this is actually achieved due to the fact that the increase in resistance within the respective resistance intervals is linear or also logarithmic.
A third advantage of the advantageous development of the resistor network consists in that, due to the resistance graduation, an extremely small number of control signals or control bits is required. This is associated with the fact that, in the resistor network according to the invention, therefore, the number of required switching elements or of required control lines is also small.
A fourth advantage of the resistor network is that the voltage over the total resistor is smaller than a factor of the two with respect to the selected resistor value.
The control signals used for driving can be advantageously, for example, control bits, that is to say digital binary control signals.
In a particularly simple and thus advantageous manner, the minimum resistance values of the respective resistance intervals can be formed with the aid of a programmable basic resistor network, the resistance value of which is determined by the first group of control signals or control bits, respectively.
The resistance values of the programmable basic resistor network, which can be determined by the first group of control signals or control bits, are preferably logarithmically graduated.
In a particularly simple and thus advantageous manner, a logarithmic graduation of the resistance values of the basic resistor network can be achieved if the basic resistor network is formed by a series connection of at least two series resistors which are logarithmically graduated.
The determination of the resistance value of the basic resistor network or, respectively, the selection of the series resistors of the series circuit of the basic resistor network can be effected in a simple and thus advantageous manner by means of a switch device which is associated with the basic resistor network. The switch device determines which of the series resistors of the series circuit are active and which are inactive by means of its switch position which is determined by the first group of control signals or control bits. The switch device thus determines the resultant resistance value of the basic resistor network.
In addition, it is considered to be advantageous if the controllable resistor network has at least two additional resistors, a single one of which is always selected by the first group of control bits. These additional resistors can then be used for ensuring the linear graduation according to the invention of the resistance elements within the respective resistance interval.
The resistance value of the additional resistor selected in each case is preferably determined by the second group of control bits.
In a particularly simple and thus advantageous manner, the at least two additional resistors can be formed in each case by a series circuit of auxiliary resistors.
The auxiliary resistors of one and the same additional resistor preferably have in each case the same resistance value in order to ensure a linear graduation of the resistance values of the additional resistors.
To produce a logarithmic graduation of the resistance intervals with respect to one another, the auxiliary resistors are logarithmically graduated from additional resistor to additional resistor.
In a particularly simple and thus advantageous manner, the resistance values of the additional resistors can be adjusted if the additional resistors are allocated switches, the switch position of which is determined by the second group of control signals or control bits and which determine which of the auxiliary resistors of the series circuit are to be active and which are to be inactive.
The additional resistors are preferably in each case connected to the switch device which selects the respective additional resistor in accordance with the first group of control signals or control bits.
The total resistance of the controllable resistor network is preferably formed by the resistance sum of the resistance value of the additional resistor selected in each case and of the resistance value of the basic resistor network.
Such a resistance sum can be formed in a simple and thus advantageous manner by series-connecting the basic resistor network and the additional resistor selected in each case.
If the controllable resistor network is intended to have a minimum resistance which is independent of the control signals or control bits, it is considered to be advantageous if the controllable resistor network has a minimum resistance or offset resistance which is connected in series with the basic resistor network and the additional resistor selected in each case.
In addition, the invention relates to a device for driving a light-emitting element, in particular a laser comprising a controllable resistor network.
With respect to such a device, the invention is based on the object of achieving that the device has a wide dynamic range and, at the same time, only a small drive increment size.
According to the invention, this object is achieved by the fact that the device exhibits a controllable resistor network according to the invention as explained.
With respect to the advantages of the device according to the invention for driving a light-emitting element, reference is made to the above statements relating to the advantages of the controllable resistor network according to the invention, since the advantages of the device according to the invention for driving the light-emitting element correspond to the advantages of the controllable resistor network according to the invention.